Electrically operated viscous fluid dispensing apparatus and method

ABSTRACT

An electrically operated fluid dispenser for dispensing a pattern of viscous fluid onto a substrate during a run mode. The dispenser is turned off and does not dispense the viscous fluid during a standby mode of operation. The dispenser includes a dispenser body having an outlet and an armature disposed in the dispenser body for movement between an opened position allowing a fluid flow from the outlet and a closed position preventing the fluid flow from the outlet. A coil is mounted adjacent the armature and selectively generates an electromagnetic field for moving the armature between the opened and closed positions. A controller includes different apparatus and methods for using the coil as a heater as well as providing other heat transfer devices on the dispensing valve to maintain a constant temperature either, during only the run mode or, during both, the run and the standby modes. 
     The above dispensing valve heating control facilitates a design of an electrically operated fluid dispenser having a body with a fluid passage intersecting first and second sides of the body and a dispensing outlet in fluid communication with the fluid passage. The dispenser includes a heater and has feed member mounted to the first side of the body with one end of the fluid passage in the feed plate fluidly connecting with one end of the fluid passage in the dispenser body. The dispenser also has an cap mounted to the second side of the dispenser body to terminate the fluid passage on the second side of the dispenser body.

This application is a Division of U.S. Ser. No. 09/533,347, entitled“Electrically Operated Viscous Fluid Dispensing Apparatus and Method”,filed Mar. 23, 2000, and is hereby expressly incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to an apparatus for dispensingviscous fluids and more specifically, to an electrically operatedapparatus for dispensing viscous liquids, such as hot melt adhesives.

BACKGROUND OF THE INVENTION

Pneumatic and electric viscous fluid dispensers have been developed fordispensing applications requiring precise placement of a viscous fluid.Pneumatic dispensers have a significant advantage in that the pneumaticsolenoid operating the dispensing valve can be made very strong, so thatthe dispensing valve operation is essentially independent of theviscosity of the fluid being dispensed. However, pneumatic dispensershave disadvantages in that they generally have a shorter life thanelectric fluid dispensers, and the operation of the pneumatic solenoidis subject to less precise control than the electric solenoid in anelectric fluid dispenser. Therefore, in some applications, electricallyoperated viscous fluid dispensers are preferred over pneumatic viscousfluid dispensers.

Generally, electrically operated dispensers include an electromagneticcoil surrounding an armature that is energized to produce anelectromagnetic field with respect to a magnetic pole. Theelectromagnetic field is selectively controlled to open and close adispensing valve by moving a valve stem connected to the armature. Morespecifically, the forces of magnetic attraction between the armature andthe magnetic pole move the armature and valve toward the pole, therebyopening the dispensing valve. At the end of a dispensing cycle, theelectromagnet is de-energized, and a return spring returns the armatureand valve stem to their original positions, thereby closing thedispensing valve.

In the operation of an electric viscous fluid dispensing gun, thecoupling between the coil and the armature is not efficient; andtherefore, in order to achieve the highest actuation speed, a currentpulse or spike is typically provided to the coil during an initialturn-on period in order to initiate the motion of the armature asquickly as possible. However, maintaining such a level of current to thecoil quickly and substantially increases coil temperature. Further,maintaining such a high level of current increases the time required forthe energy stored in the coil's inductance to dissipate, therebyincreasing the turn-off time and the time required to close the fluiddispenser. Therefore, after the initial current spike, the currentthrough the coil is normally reduced to approximately the minimum valuerequired to hold the armature in its open position by overcoming theopposing force of the return spring. Such a stepped current waveform isuseful in reducing the current induced heat load in the coil, therebyallowing the coil to operate at a lower temperature than if the steppedwaveform were not used. However, as is described below, the operation ofthe coil and armature during the fluid dispensing process creates otherheat related issues that impact the quality of the fluid dispensingprocess.

The continued development and use of viscous fluid electric dispensershas resulted in more demanding performance specifications as well as agreater understanding of how heat in the dispenser can potentiallyeffect performance. For example, the electric coil of an electricdispensing valve normally is not capable of providing the same forces asa pneumatic solenoid and therefore, is more subject to changes inresistance to valve stem motion that may be caused by changes inviscosity of the fluid being dispensed. Thus, as the viscosity of thefluid being dispensed changes, the load on the electromagnetic coilchanges, and the time required to open and close the dispensing valvewill likewise change. Such changes in timing of the dispensing valveopening and closing will change the location of the adhesive beingdispensed on the substrate.

In addition to the above, newer applications have more demandingperformance specifications and require ever-increasing gun speeds, thatis, a shortening of the time required to open and close the dispensingvalve. The operational speed of the dispensing valve can be increased byincreasing the electrical power applied to the electric coil operatingthe valve. The electrical power is normally increased by increasing thecurrent being supplied to the coil which also adds heat to the coil,thereby causing the temperature of the coil to rise. A hotter or highercoil temperature impacts the consistency of the viscous fluid dispensingin several ways. First, heat from the coil is conducted through thearmature and the valve stem which is adjacent the valve seat and issurrounded by the viscous fluid. As the temperature of the armaturefluctuates, for example, goes up, the viscosity of the fluid to bedispensed likewise fluctuates and, in this example, decreases, therebychanging the flow of the viscous fluid from the dispenser.

Second, the speed at which the armature can be moved between the openand closed positions is a function of the rate of change of current inthe coil, which, in turn, is controlled by the electrical time constantof the coil. The electrical time constant is a function of the coilresistance which, in turn, is a function of temperature. The coilutilized in the viscous fluid dispenser discussed herein can experiencean approximately 50% variation in resistance over its normal range ofoperating temperature. Such a change in resistance substantially affectsthe electrical time constant of the coil, thereby similarly affectingthe speed at which the coil can open and close the valve.

The thermal time constant of the coil is a function of the coil mass andits thermal connections to surrounding materials such as the gun bodyand ambient temperature. The thermal time constant of the coil and itssurrounding thermal system affects the time required for the thermalsystem to reach a steady state condition. When the dispensing system isrunning at a constant speed, and a steady state condition is achieved,the thermal time constant normally does not present a source ofvariation in the operation of the dispensing coil. However, the steadystate condition can change for several reasons, for example, if theproduction line speed is either increased or decreased or, thedispensing gun is not operating and in the standby mode. Either of thoseconditions causes the coil temperature to change, and the thermal timeconstant presents a source of variations in the operation of the viscousfluid dispenser.

Of further concern is the maximum temperature rating of the coil wireinsulation. Under normal operating conditions, the temperature rating ofthe wire insulation exceeds the wire temperature. However, in a worsecase situation, if the temperature of the wire exceeds the temperaturerating of the wire insulation, the integrity of the coil wire insulationmay be compromised, thereby causing coil windings to short-circuittogether. Any coil windings that short-circuit together will change theresistance of the coil and potentially adversely effect the consistencyof the fluid dispensing operation of the dispenser.

Thus, by using a stepped current waveform, known electric fluiddispensers attempt to reduce the temperature of the coil. Further, it isknown to utilize a heater in a manifold to which the fluid dispenser ismounted to control the temperature of the fluid circulating through themanifold and the fluid dispenser, thereby indirectly controlling thetemperature of the dispenser itself. However, as will be appreciated,there have been no attempts to control the temperature of the fluiddispenser directly with a self contained device in order to maintain theelectric fluid dispenser at a constant temperature.

SUMMARY OF INVENTION

The present invention provides an improved electric dispenser forviscous fluids that manages the thermal condition of the dispenserdirectly to provide a substantially improved, more consistent dispensingof viscous fluids. The electric dispenser of the present inventionprovides more consistent actuation of the dispensing valve independentof changes in the speed of operation of the dispenser. The electricfluid dispenser of the present invention reduces the range oftemperature fluctuations resulting from changes in speed of theproduction line and changes in the frequency of operation of the fluiddispenser. Further, the electric fluid dispenser of the presentinvention maintains a generally constant coil temperature independent ofthe rate of gun operation. Providing a fluid dispenser that has aself-contained temperature control that reduces the range of temperaturevariations helps to maintain the viscosity of the fluid within thedispenser constant. By better controlling the temperature within theelectric viscous fluid dispenser, a more consistent, faster and reliableoperating cycle is achieved. Thus, the electric dispenser of the presentinvention provides the advantage of dispensing a viscous fluid moreaccurately, precisely and with a higher quality than was heretoforepossible.

In accordance with the principles of the present invention and thedescribed embodiments, the invention in one embodiment provides anelectrically operated fluid dispenser for dispensing a viscous fluidonto a substrate during a run mode. The dispenser includes a body havingan outlet and an armature disposed in the dispenser body for movementbetween an opened position allowing a fluid flow from the outlet and aclosed position preventing the fluid flow from the outlet. A coil ismounted adjacent the armature and selectively generates anelectromagnetic field for moving the armature between the opened andclosed positions. A controller is connected to the coil and providesoutput signals to energize a coil positioned with respect to an armaturewithin the fluid dispenser with a drive current to actuate the fluiddispenser and to simultaneously maintain the coil at an approximatelyconstant temperature during the run mode.

In one aspect of the one embodiment, the controller includes powerswitches providing a drive current signal to the coil and a thermalcontroller providing a current waveform signal to the power switches.The current waveform signal operates the power switches to maintain thecoil at a constant temperature in response to a temperature controlloop.

In another aspect of the one embodiment, a heat transfer device ismounted in a heat transfer relationship with the dispenser body; and thecontroller is connected to the heat transfer device to cause the heattransfer device to selectively transfer heat between the heat transferdevice and the dispenser body during the run and standby modes, therebymaintaining the dispenser body at a constant temperature during the runand standby modes.

In a second embodiment of the invention, the dispenser is turned off anddoes not dispense the viscous fluid during a standby mode of operation;and the controller provides further output signals to energize the coilwith a current to maintain the coil at an approximately constanttemperature during the standby mode.

In another embodiment of the invention, the coil has first and secondwindings disposed adjacent the armature, the controller selectivelyprovides output signals to the first and second windings of the coil tocause current flow in the coil windings during the run and standbymodes. The controller further includes a switching apparatus selectivelyplacing the first and second windings in an additive relationship duringthe run mode to move the armature between the opened and closedpositions and in an opposing relationship during the standby mode tomaintain the armature immobile in the closed position.

In one aspect of this other embodiment, the controller includes powerswitches providing a drive current signal to the coil; and a thermalcontroller provides a current waveform signal to the power switches. Thecurrent waveform signal operates the power switches to maintain the coilat a constant temperature. The thermal controller generates the currentwaveform signal in response to changes in either power, current ortemperature variables with respect to a respective desired value ofthose variables.

In another aspect of this other embodiment, the controller includes ahigh frequency power supply and a switching device connected between thepower switches, the coil and the high frequency power supply. Theswitching device connects the coil to the power switches during the runmode and connects the coil to the high frequency power supply during thestandby mode.

In a further aspect of this other embodiment, the controller includespower switches for connecting the coil windings in parallel across apower supply to permit the duty cycle of the current flow in each of thecoil windings to be individually controlled, thereby uncoupling andindependently controlling the power heating of the coil from theactuation power provided by the coil windings.

In a still further embodiment of the invention, a method is provided foroperating an electric viscous fluid dispenser to maintain a coilpositioned with respect to an armature within the dispensing gun at anapproximately constant temperature during the run mode by heating thecoil. In an additional embodiment, the above method includes maintainingthe coil at an approximately constant temperature while the viscousfluid is not being distributed during a standby mode by heating the coilduring the standby mode. In different aspects of this invention, thecoil is heated during the run and standby modes by current flowingthrough the coil or by a separate heating and cooling heat transferdevice. In a further aspect of the invention, the heating of the coil iscontrolled by an RMS value of the current in the coil.

The above embodiments of a fluid dispenser temperature controller havethe advantages of reducing the range of temperature variations withinthe fluid dispenser and normally, maintaining the temperature of thefluid dispenser approximately constant. Thus, the fluid dispensertemperature controller does not rely on the user being able to controlthe best current waveform parameters, but instead, is adaptive andself-adjusting to maintain a constant coil temperature. The activetemperature control protects the coil from overheating in the event thatthe user adjusts the current waveform such that an excessive temperaturewould otherwise be produced. With a constant coil temperature, theviscosity of the fluid within the dispensing gun is held moreconsistent, thereby improving the consistency of the dispensing process.Further, by maintaining the constant temperature over the full range ofoperating frequency of the dispensing gun, the coil temperaturecontroller provides a further advantage of providing a higher qualityand more consistent viscous fluid dispensing operation. In addition,such a temperature control permits the dispensing gun to be consistentlyoperated at a rate that is very close to, if not at, the theoreticalmaximum temperature limit of the gun without overheating.

In a further embodiment of the invention, an electrically operated fluiddispenser has a body with a heater and a fluid passage intersectingfirst and second sides of the body and a dispensing outlet in fluidcommunication with the fluid passage. The dispenser includes a feedmember having a fluid passage intersecting ends of the feed plate. Oneend of the feed member is mounted to the first side of the body with oneend of the fluid passage in the feed member fluidly connecting with oneend of the fluid passage in the body. The dispenser also has a capmounted to the second side of the body to terminate the fluid passage onthe second side of the body.

In one aspect of this further embodiment, the dispenser includes asecond dispenser with a body having a heater, a fluid passageintersecting first and second sides of the second body and a dispensingoutlet in fluid communication with the fluid passage. The first side ofthe second body is mounted to the second side of the first body with oneend of the fluid passage in the second dispenser body fluidly connectingwith an opposite end of the fluid passage in the first dispenser body.

In other aspects of this further embodiment, the dispenser includes aspacer plate disposed between the first and second bodies, and theheater is comprised of either a coil mounted with respect to an armaturewithin the body or, a heating and cooling heat transfer device.

This further embodiment of the invention with the use of the coil heaterhas the advantage of maintaining the viscous fluid within the passage atthe desired temperature without requiring a separate fluid distributionmanifold plate to which the dispensing gun is normally mounted. Adispensing gun of this construction has the further advantage of beingsubstantially more compact than the traditional manifold plate design.Further, the construction of the dispensing gun is substantially lessexpensive; and its simpler construction provides substantially greaterflexibility in mounting the dispensing gun with associated equipment.

In yet another embodiment of the invention, a temperature monitor formonitoring a temperature of an electrically operated fluid dispenser hasa coil mounted adjacent an armature within the dispenser, the coilselectively generates an electromagnetic field to move the armaturebetween opened and closed positions. The temperature monitor includescurrent measuring apparatus for measuring a current in the coil and acomparator for comparing a measured current value to a desired currentvalue. An indicator provides an indication representing a relationshipbetween the measured current value and the desired current value.

In different aspects of this embodiment, the temperature monitormeasures the RMS value of the current in the coil and has differentindicators for providing different indications representing differentvalues of the measured current relative to a desired current value.

The thermal monitor has the advantage of providing the user with a realtime indication of whether the user's adjustments to the currentwaveform provide a coil temperature that is less than, close to or inexcess of the maximum coil temperature. In addition, the thermal monitorhas the further advantage of helping the user select the temperaturelimits which are appropriate for the dispensing gun being used and thedispensing application being effected.

Various additional advantages, objects and features of the inventionwill become more readily apparent to those of ordinary skill in the artupon consideration of the following detailed description of thepresently preferred embodiments taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an axial cross-sectional view of an electrically operatedfluid dispenser constructed according to the invention; and

FIGS. 2A-2D are schematic diagrams of current waveform signals used toprovide a drive current signal to the coil of the dispensing valve ofFIG. 1.

FIG. 3 is a schematic block diagram of a gun controller that includes athermal controller for controlling the temperature of the dispensingvalve coil in accordance with the principles of the present invention.

FIG. 4 is a schematic block diagram of one embodiment of the thermalcontroller of FIG. 3.

FIG. 5 is a flow chart illustrating process steps associated with thelearn mode of the gun controller.

FIG. 6 is a schematic block diagram of another embodiment of the thermalcontroller of FIG. 3 utilizing a current setpoint.

FIGS. 7A and 7B are schematic block diagrams of further alternativeembodiments of the thermal controller of FIG. 3 that utilize atemperature control loop.

FIG. 8 is a schematic block diagram illustrating a second embodiment ofa gun controller for controlling the temperature of the dispensing valvecoil in accordance with the principles of the present invention.

FIG. 9 is a schematic block diagram of a further embodiment of a guncontroller for controlling the temperature of the dispensing valve inaccordance with the principles of the present invention.

FIG. 10 is a partially disassembled view of a dispensing gun utilizingthe coil heating capabilities of the present invention.

FIG. 11 is a schematic diagram of an embodiment utilizing an integratedcircuit chip to detect temperature variations in the dispensing valvecoil.

FIG. 12 is a schematic diagram of an alternative embodiment forinterconnecting coil windings of a bifilar coil.

FIG. 13 is a schematic block diagram of an alternative embodiment of agun controller with a thermal controller for controlling the temperatureof the dispensing valve coil in accordance with the principles of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first to FIG. 1, an electrically operated viscous fluiddispenser or dispensing gun 10 comprises one or more dispensing modulesor valves 33 mounted on a fluid distribution manifold plate 45 in aknown manner. The dispensing valve 33 includes a dispenser body 12 and afluid dispensing nozzle body 14. The dispenser 10 is adapted fordispensing high viscosity fluids, such as a hot melt adhesive, but otherdispensed fluids can benefit from the invention as well. Such otherfluids include soldering fluxes, thermal greases, heat transfercompounds and solder pastes. Furthermore, the dispenser 10 is mounted ina dispensing machine or system (not shown) in a known manner to dispensefluids in discrete amounts, preferably as droplets or dots, butalternatively in continuous beads. As shown in FIG. 1, the dispenserbody 12 used in conjunction with the fluid dispensing nozzle body 14 isparticularly constructed to dispense droplets 18 of the viscous fluidonto a substrate 19. Relative motion between the substrate 19 anddispenser 10 is provided in a known manner.

A valve stem 26 is mounted in an interior portion 20 of the dispenserbody 12, and the valve stem includes a shaft 28 through the interiorportion 20. A ball 30 is mounted to a lower end 28 a of the shaft 28which is shown in FIG. 1 in sealing engagement with a valve seat 32positioned in the nozzle body 14. Thus, the valve stem 26 and ballreciprocate between opened and closed positions with respect to thevalve seat 32, thereby operating as a dispensing valve 33. With the ball30 sealingly engaging valve seat 32, high viscosity fluid, such as anepoxy, cannot flow through an outlet 34 in the valve seat 32. The nozzlebody 14 also has a nozzle tip 36 with an orifice 38 aligned with theoutlet 34 and flush mounted to the valve seat 32 by a threaded retainingnut 40. The nozzle tip 36 can be readily exchanged with a differentnozzle tip to produce droplets of a different size and, in some cases, adifferent shape.

A fluid inlet passageway 46 intersects the interior portion 20 and isconnected to a fluid passage 49 in the manifold 45 which in turn isfluidly connected to a source 47 of hot melt adhesive which normally ispressurized. Arrows 50 indicate the flow path of the fluid enteringthrough the fluid inlet passageway 46 and through the interior portion20.

An armature 60 is disposed within the interior portion 20 and iscoaxially aligned with and, preferably, formed integrally with shaft 28.An electromagnetic coil 70 is disposed about the armature 60. Althoughany suitable electromagnetic coil could be used, it is contemplated thatthe electromagnetic coil 70 will be generally toroidal in shape. Thecoil 70 is contained in a housing 72 and connected to a power source(not shown). When supplied with electrical current, the coil 70generates an electromagnetic field which actuates the valve stem 26 toan open position as will be described below.

A bore 80 extends into the armature 60 to house a return spring 82. Thereturn spring 82 biases the valve stem 26 and, more specifically, theball 30, to sealingly engage the valve seat 32 in a closed position. Thereturn spring 82 is normally a compression spring which is placed undercompression within the bore 80 through engagement with anelectromagnetic pole 84. To achieve an opened position, theelectromagnetic coil 70 must generate a sufficient electromagnetic fieldbetween the armature 60 and the pole 84 so as to attract the armature 60and the pole 84 together. Since the pole 84 cannot move, the armature 60will move against the force of the spring 82 until it hits the pole 84.The stroke length is the distance between the armature 60 and the pole84 as shown in FIG. 1. An adjustment nut 86 provides a means toinitially set the stroke length. More specifically, brazing 88 connectsthe pole 84 to a tubular member 90. The tubular member 90 has a lowerthreaded portion 92 received within an internally threaded lower housingportion 94. A tool, such as a screwdriver, may be used to turn the pole84 and, therefore, the tubular member 90, as an O-ring 96 slides againstan interior surface of the lower housing portion 94. This adjustmentvaries the distance between the lower end of the pole 84 and the upperend of the armature 60 or, in other words, varies the stroke length ofthe valve stem 26. A lower donut 98 is disposed about the tubular member90 and rests against an upper side of the lower housing portion 94 whilean upper donut 100 is held against the coil housing 72 by the nut 86 anda lock washer 102. Such a dispenser 10 is further described incommonly-assigned, U.S. Pat. No. 5,875,922, entitled APPARATUS FORDISPENSING AN ADHESIVE, issued on Mar. 2, 1999, which is herebyincorporated by reference herein in its entirety.

As previously discussed, electric guns are preferred because of theprecision with which they may be controlled during a manufacturingoperation. However, electric guns have a disadvantage in thattemperature variations within the gun directly effect the guns'performance. Further, known electric fluid dispensers apply a steppedcurrent waveform to the coil that has an initial spike and then stepsdown to a magnitude sufficient to hold the valve stem 26 in its openposition by overcoming the opposing force of the return spring 82. Aseries of such current waveform signals is schematically illustrated inFIG. 2A. To turn the gun on, thereby opening the dispensing valve 33, aninitial current magnitude I_(pk) is applied for a duration or period oftime T_(pk) in response to a trigger pulse. Thereafter, the current isreduced to a lesser hold level I_(h) for the remaining period of theon-time T_(on). The zero current value is then maintained for anoff-time T_(off) during the remaining time of the current waveformperiod T_(p). As will be appreciated, the waveform illustrated in FIGS.2A-2D is for purposes of discussion and the real waveform consists ofexponential functions that transition the current between levels. Thereal time on-time wave shape can look radically different from theidealized waveform of FIG. 2A-2D, depending on many factors such asI_(pk), I_(h), T_(pk), T_(on), T_(p), L_(coil), R_(coil), etc. TheT_(on) and T_(p) are related to the adhesive pattern required for aparticular product. The inductance and resistance of the coil are afunction of the gun itself, and the I_(pk) is normally bounded by thelimits of magnetic saturation of the dispensing gun 10.

The current waveform period T_(p) is inversely related to frequency.Thus, as the frequency of the trigger pulses increases, the period T_(p)of the current waveform decreases. Thus, over time, coil heating is afunction of the frequency of operation of the dispensing gun 10, thepeak current magnitude I_(pk), the duration of the peak current T_(pk),the magnitude of the hold current I_(h) and the current waveform on-timeT_(on). Initial values of magnitudes of the peak and hold currents arebased on the coil specifications, however, the peak current magnitudeI_(pk), the magnitude of the hold current I_(h) and the duration of thepeak current T_(pk) are all adjustable by the user. The user oftenadjusts the current waveform and the dispensing line rate in order totune the dispensing operation to its peak performance. However, the userhas no real time feedback as to the effects of such adjustments on thecoil temperature which, as discussed earlier, can have adverse effectson the quality of the dispensing process. Thus, such system tuning isalso influenced by other constantly changing conditions which make suchadjustments not repeatable and somewhat of an art form.

The present invention actively controls the current waveform parametersover substantially the full range of operation of the dispensing gun 10,so that the coil temperature is maintained at a constant value less thana maximum coil temperature. If coil temperature is maintained constantfor different triggering frequencies, the adverse effects of changes incoil temperature are eliminated, thereby providing a more consistent andprecise viscous fluid dispensing operation.

One embodiment for regulating coil temperature is illustrated in FIG. 3in which the coil 70 is a bifilar coil, that is, a coil having twoindependent coil windings 110, 112. The coil windings are connected by aswitching device 114 which can be implemented using switching relay orsemiconductor switches such as MOSFET, IBGT, BJT, etc. In FIG. 3, theswitching device 114 is illustrated as a switching relay comprised ofswitching contacts 116 and a switching solenoid 118. During a run modeduring which fluid is being dispensed, the switching device 114 connectsthe coil windings 110, 112 via the contacts A such that the first coilwinding 110 is in series with the second coil winding 112, and thecurrent therethrough flows in a common direction with respect to thecoil polarity of the coil windings 110, 112. In a standby mode, thedispensing gun 10 is inactive; and therefore, in response to a standbysignal, the switching device 114 switches the coil winding 112 tocontacts B, thereby connecting the coil windings 110, 112 in opposition.Thus, during the standby mode, current flows through coil winding 110 inone direction with respect to its coil polarity, however, current flowsin the opposite direction in winding 112 with respect to its coilpolarity. The flux fields created by windings 110 and 112 oppose andcancel each other. With a net flux of zero, the current flow through thecoil 70 is unable to overcome the force of the return spring 82.Consequently, during the standby mode, the armature is maintainedimmobile in the presence of current flow through the coil 70, and thedispensing valve 33 remains in its closed position. Consequently, asubstantially constant current flows through the coil 70 at all timesindependent of the dispensing operation of the dispensing valve 33,thereby maintaining a substantially constant temperature within the coil70.

Referring to FIG. 3, the coil 70 is connected to a gun controller 120including a power supply 122, a coil current modulator 124, a thermalcontroller 126 and a current sensor 128. The current sensor 128 canimplement one of many current measuring methods including using a simpleresistor, a Hall effect device, a current transformer, etc. The guncontroller 120 is further connected to a machine or system control 130and provides output signals to warning and fault indicators 132 whichmay be included within the gun controller 120 or a part of otherdevices, for example, the system control 130. The system control 130includes all of the other known dispensing system or machine controlsnecessary for the operation of the dispensing system. The system control130 also includes input devices such as a keypad, pushbuttons, etc. andoutput devices such as a display, indicator lights, etc. that providecommunication links with a user in a known manner. The thermalcontroller 126 can be implemented using analog or digital circuitcomponents; however, the thermal controller is normally implemented witha programmable microcomputer control that operates in response to storedprogram instructions as well as signal inputs to the controller 126.

In this embodiment of the invention, in order for the temperature of thecoil 70 to remain constant, the power being supplied to the coil shouldalso be constant. The power to the coil can theoretically be no morethan the power being supplied to the coil with the production linerunning at its maximum rate. In order to determine that power value, thegun controller 120 executes a learn mode of operation which is typicallyinitiated by the user actuating a switch on the system control 130 thatprovides a learn signal on an output 130 to the gun controller 120. Aschematic functional block diagram of one embodiment of a portion of thethermal controller 126 is illustrated in FIG. 4. The thermal controller126 includes a power control 137 that is implemented with a programmablemicroprocessor control having programmed instructions to implement thedevices shown within the control 137. The learn mode process executed bythe thermal controller of FIG. 4 is illustrated by the flow chartillustrated in FIG. 5. The first step, at 502, of the learn mode processis to operate the dispensing gun 10 at its maximum rate. Normally, thesystem control 130 is used to run the production line at its maximumrate which, in turn, causes the dispensing gun 10 to also operate at itsmaximum rate.

The dispensing gun 10 is operated in response to a trigger pulse suppledon output 131 from the system control 130. With each trigger pulse, awaveform signal, as illustrated in FIG. 2A, is provided by a waveformgenerator 148. The waveform signal, for example, a current waveform,determines the waveform of an output signal, for example, a drivecurrent, that is provided by the coil current modulator 124. The valuesof I_(pk) and T_(pk) are generally chosen as a function of the viscosityof the fluid being dispensed. Further, the value of the hold currentI_(h) is set to a nominal value equal to the minimum current required tohold the valve in the open position, that is, the minimum value ofcurrent to overcome the biasing force of the compressed spring 82 (FIG.1). That current waveform passes through the D/A converter 149 and fromthe thermal controller 126 on an output 151. The current waveform thendrives power switches 154 in the coil current modulator 124 to providethe desired current or power from the power supply 122 to the coil 70.Thus, the dispensing valve 33 is operated at the maximum frequency thatwould be expected in the current application. Alternatively, it may bepossible to use the system control 130 to operate the dispensing valve33 independently of the production line. Next, at 503, the rate at whichtrigger pulses are being generated at the maximum frequency is stored inthe system control 130. As will be appreciated, this process step isoptional depending on how current is applied to the coil in the standbymode of operation.

When operating in the learn mode, the maximum current or power beingconsumed by the dispensing gun 10 must be identified to establish apower target or setpoint for the control of the gun during the run ordispensing mode of the dispensing gun 10. Thus, the next step 504 in thelearn mode is to measure the current flow through the coil 70 while thegun is operating at its maximum rate. In one aspect of the invention,the current is measured by a current sensor 128, and a measured currentvalue on an output 129 is provided to the controller 126 by means of anA/D converter 136 of FIG. 4. The digital current value from the A/Dconverter 136 is then sampled, averaged and stored. The RMS value of thecurrent or the voltage at the coil is a measure of the heating power inthe coil. Therefore, normally, the RMS value of the current is computed,which provides a value that is very representative of the temperature ofthe coil. As is appreciated, computing the RMS value of the currentconsumes significant resources within the control 137. Therefore,alternatively, the current sensor 128 output can be input to anintegrated circuit chip that senses the current and provides a DCvoltage output having a magnitude value proportional to the RMS value ofthe sensed current. Such an integrated circuit chip is illustrated aschip 180 in FIG. 11, and an output 188 from the chip 180 is then aninput to the A/D converter 136.

The learn mode at 506 then requires a computation of the coil power atthe maximum gun operating rate. The coil power is determined within thecontroller 126 by a current-to-power converter 138. As will beappreciated, any known relationship between current, voltage, coilresistance and power may be used to compute the power, however, thepower is normally computed utilizing the formula P=I² _(coil)×R_(coil).Thus, the resistance of the coil is required for the power computation.The resistance of the coil can be determined in one of several ways.First, a previously determined and stored coil resistance value can beread from a store (not shown) within the processor 126 and used in thecurrent-to-power conversion. However, as discussed earlier, theresistance of the coil is a function of the coil temperature. Therefore,alternatively, a table correlating coil temperature to coil resistancevalues may be stored in the controller 126, and a temperature sensor139, shown in phantom in FIG. 3, mounted in a heat transfer relationshipwith the coil 70 can be used to detect the temperature of the coil. Inthis aspect of the invention, the temperature sensor 139 is read by thecontroller 126 and a comparable coil resistance read from the table.

Alternatively, the resistance of the coil can be calculated in real timebased on temperature measurements from the sensor 139 in accordance withthe equation R_(h)=R_(c)(1+α(T_(h)−T_(c))), where R_(h) and R_(c) arethe respective hot and cold resistances of the coil; T_(h) and T_(c) arethe respective hot and cold temperatures of the coil; and α is thecoefficient of thermal resistance of copper, that is, 0.00218/° F. Apreproduction cold resistance of the coil R_(c) is determined at T_(c)by applying minimal power to the coil and calculating R_(c) as the ratioof an applied voltage to a measured current. The T_(c), R_(c) and alphavalues are stored, and at selected times during the run mode, thetemperature of the coil T_(h) is measured with the sensor 139, and theabove formula is used with the stored values to calculate the resistanceof the coil R_(h).

In a further alternative, the resistance of the coil can be measured inreal time by other methods. For example, referring to FIG. 2B, duringthe off-time T_(off) of the current waveform, the control circuitprovides a sample current pulse to the coil 70; and the coil current andvoltage are measured in a known manner. The resistance value of the coilcan then be computed from the samples of voltage and current inaccordance with Ohm's Law. FIG. 2C illustrates another method in whichduring the off-time T_(off) of the current waveform, a small, non-zero,substantially constant magnitude current waveform is applied to the coil70. In a similar manner, the coil current and voltage are measured andused to compute the resistance of the coil 70. The magnitude of thesmall, nonzero current of FIGS. 2B and 2C is less than the magnitude ofthe hold current, so that the even though the coil is electricallyturned-on, the spring force maintains the coil 70 mechanicallyturned-off.

Coil resistance can be measured using a still further alternativeillustrated in FIG. 2D in which a sine wave is applied to the coil 70during the off-time T_(off) of the current waveform. The sine wave has apeak-to-peak value that is less than the magnitude of the hold current,so that the coil 70 is electrically on but mechanically off. Further,the sine wave normally has a frequency of approximately 67 Hertz, but aswill be appreciated, other frequencies may be used. The coil 70 is acombination of an inductance and a resistance. With a pure inductancethe voltage waveform leads the current waveform by 90°. However, theresistance component of the coil 70 will proportionally reduce theamount by which the voltage waveform leads the current waveform. Thatlead time can be determined by detecting a zero crossing of the voltagewaveform on output 123 of the power switches 154 (FIG. 3) that isapplied to the coil 70. That zero crossing is used to start a timer orcounter (not shown) in the thermal controller 126; and thereafter, thenext zero crossing of the current waveform as detected on the output 129of the current sensor 128 is used to stop the counter. That measuredtime shift can be used in conjunction with a table correlating timeshift to coil resistance values to determine a current resistance of thecoil 70. The table of time shift versus coil resistance values iscreated experimentally. In a preproduction test using the coil 70, theresistance and temperature of the coil 70 can be measured withinstrumentation in response to operating the coil at different powerlevels and hence at different temperatures. The time shift can bemeasured and recorded in the manner described above, and a table of timeshift versus coil resistance and temperature created and stored.

After the coil power at the maximum dispensing rate is computed, thelearning process, at 508 of FIG. 5, then causes the control 137 to setthe power setpoint or target equal to the computed coil power value.Thus, the maximum dispensing rate is going to produce a desired maximumtemperature of the coil 70, and the power or target setpoint iscorrelated to and representative of that maximum temperature.Consequently, maintaining the power in the coil equal to the powersetpoint will result in the coil 70 being maintained at a constanttemperature equal to the desired maximum temperature. The learningprocess further, at 510, determines whether the power setpoint isgreater than a predetermined and stored maximum value; and if so, at512, a warning indicator 132 is activated.

After the power setpoint has been determined in the learn mode, the guncontroller 120 is ready to begin operation in one of two operationalmodes, that is, a run mode or a standby mode. One of those modes isnormally selected by a signal on output line 140 from system control 130in response to a user input or selection. In the run mode, the thermalcontroller 126 causes the switching device 114 to connect the coilwinding 112 to contacts A, thereby connecting the contact windings 110,112 in series. In this connection, the flux generated by the currentflowing through the coil windings 110, 112 is in the same direction andeffective to operate the armature 60 of the dispensing valve 33. When inthe standby mode, the switching device 114 switches the connections ofthe coil winding 112 to the B contacts, thereby placing the coilwindings 110, 112 in opposition. The flux generated by current flowthrough the coil windings 110, 112 is in opposition and in a cancelingrelationship. Thus, with little or no net flux, the current through thecoil windings 110, 112 is incapable of moving the armature of theviscous fluid dispenser 10.

Assuming the dispenser 10 is operating in the run mode, a measuredcurrent signal from the current sensor 128 is provided to the A/Dconverter 136 of the thermal controller 126. In a manner as previouslydescribed, the value of the current is used with the coil resistance todetermine a power value in the current-to-power converter 138. Thatpower value is then compared or algebraically summed in a comparator orsumming junction 141 with the power setpoint determined during the learnmode. The difference between the currently measured power value from theconverter 138 and the power setpoint is provided as an error signal onoutput 142 from the comparator 141. If the measured power is greaterthan the power setpoint, a warning indicator 132 may be activatedindicating to the user that the selected current waveform parameters areproducing a coil temperature in excess of the selected maximum coiltemperature. Thus, the user can then modify the current waveformparameters until the warning indicator is deactivated, thereby assuringthe user that the current waveform is producing a coil temperature lessthan the maximum temperature.

The error signal on output 142 is input to a feedback controller 144which is normally implemented using a proportional-integral-derivative(“PID”) in a known manner. However, as will be appreciated, othercontrol schemes may be used. An output signal from the feedbackcontroller 144 is provided to a power-to-current converter 146. Thepower value is converted to a current value utilizing knownrelationships as described with respect to the operation of thecurrent-to-power converter 138. In other words, given a power value fromthe feedback controller 144 and a coil resistance value, a current valueis readily determined.

That current value is then supplied to a waveform generator 148 which,in turn, is initiated by a trigger pulse on output 131 of the systemcontrol 130. The trigger pulse defines the point in time at which thecurrent waveform is to be supplied to the coil 70, thereby opening thedispensing valve 33. The trigger pulses are normally produced within thesystem control 130 by a known pattern controller or programmable limitswitch (not shown). The pattern controller stores a matrix of valuesthat represent the operation of various dispensing guns to provide thedesired dispensing operation. The generation of a trigger pulse toinitiate the operation of a dispensing gun 10 is determined by arelative position of a detectable feature or portion of the substrate 19with respect to the dispensing gun 10. That relative position can bedetermined and tracked by utilizing the pattern controller orprogrammable limit switch in a known manner. Thus, in response to eachtrigger pulse, the waveform generator 148 provides an output to controlthe operation of a D/A converter 149 in such a manner as to provide thestepped waveform illustrated in FIG. 2.

In producing the stepped waveforms of FIGS. 2A-2D, the waveformgenerator 148 normally chooses values of I_(pk) and T_(pk) as a functionof the viscosity of the fluid being dispensed. In some applications, itmay be appropriate to assume that the viscosity of the fluid remainsconstant; and therefore, the values of I_(pk) and T_(pk) may be chosenand remain fixed throughout the dispensing cycle. In other controlsystems, it is known to provide signals representing changes inviscosity. A table of I_(pk) and T_(pk) values associated with differentviscosity values may be established and the appropriate I_(pk) andT_(pk) values chosen as a function of a currently determined viscosityvalue. The dispensing on-time T_(on) varies as a function of theoperating speed of the dispensing system within which the dispensing gun10 operates. Further, the value of the hold current I_(h) is nominallyset to a value equal to the minimum current required to hold the valvein the open position, that is, the minimum value of current to overcomethe biasing force of the compressed spring 82 (FIG. 1).

If the dispensing system is operating at its maximum rate, the currentbeing detected by the current sensor 128 results in a power value thatis substantially equal to the power setpoint; and hence, there is a zerodifference signal on the output 142 from the summing junction 141.Therefore, in that situation, theoretically no modification of thecurrent waveform driving the coil 70 is required. However, as will beappreciated, the dispensing system may often be operated at a rate thatis less than the maximum operating rate. In those situations, thecurrent measured by the current sensor 128 will result in a power valuefrom the converter 138 that is less than the power setpoint. If the coilis operated at that lesser current value, the temperature of the coilwill drop from the temperature it had achieved during operation atmaximum rate. That lesser temperature changes the resistance of the coil70 and further results in a decrease in the temperature of the coil. Thedisadvantages of such temperature variations have previously beendiscussed. Therefore, in accordance with the principles of the presentinvention, if the RMS current value provided to the summing junction 141decreases, it is desirable to subsequently increase the RMS currentvalue being supplied to the coil 70 so that the power being consumed bythe coil 70 remains substantially constant and equal to the powersetpoint. Thus, the current waveform functions to provide a drivecurrent to the coil 70 (FIG. 1) that first, moves the valve stem 26 toopen the dispensing valve 33 and dispense the viscous fluid and second,simultaneously varies current in the coil 70 to maintain a substantiallyconstant temperature.

The analog current value on the output 151 of the D/A converter 149 isprovided to a coil current modulator 124 (FIG. 3). The modulator 124includes a comparator or summing junction 150 having inputs responsiveto the output 151 of the D/A converter 149 and the output 129 of thecurrent sensor 128. The summing junction 150 provides an output 152 thatis an error signal representing the difference between those two currentvalues. That error signal is used to provide a pulse width modulation ofthe power switches 154 in a known manner. The power switches 154 operateto provide a desired drive current signal to the coil 70 but with acurrent waveform having a general shape corresponding to the shapedetermined by the waveform generator 148. The coil switches are normallysemiconductor switches such as, for example, MOSFET switches or bipolartransistors which can be configured in known H-bridge or other switchingcircuit.

If the dispensing system is operating at less than its maximum rate,heat may be added to the coil 70 in one of several different ways.First, the waveform generator 148 increases the value of the holdcurrent I_(h) in response to an output from the feedback controller 144.As the hold current increases, the current sensor 128 will detect anincrease in the current value which, in turn, will increase the valuefrom the power converter 138. That process is iterated until the powervalue from the power converter 138 is equal to the power setpoint andthe error signal on the output 142 of the summing junction 141 has anapproximately zero value. Alternatively, the waveform generator 148 canincrease the time width T_(pk) of the peak current I_(pk). As a thirdalternative, the waveform generator 148 can also increase the magnitudeof the peak current I_(pk) in response to an error signal on the output142 of the summing junction 141. The extent to which the peak currentcan be varied is a function of the current required to saturate themagnetic circuit. As will be appreciated, the waveform generator 148 canmodify one or more of the above variables in a desired pattern tocontrol the current being supplied to the coil 70.

Thus, in accordance with the above, the gun controller 120 is effectiveto maintain the power and hence, the temperature, of the coil 70substantially constant, independent of the operating frequency of thedispensing gun 10 during the run mode. Thus, the current waveformfunctions to provide an appropriate drive current to the coil 70(FIG. 1) that first, moves the valve stem 26 to open the dispensingvalve 33 and dispense the viscous fluid and second, simultaneouslyvaries current in the coil 70 to maintain a substantially constanttemperature. Therefore, the gun controller 120 of FIG. 3 not onlyprovides the proper current waveform to actuate the fluid dispensinggun, but it introduces heat into the coil in a controlled manner toreduce the range of temperature variations that would otherwise beexperienced by the fluid dispenser.

At a subsequent time, the user will switch the system from the run modeinto the standby mode. The state of the signal on output 140 of thesystem control changes, which causes the thermal controller to changethe state of operation of the switching solenoid 118, thereby switchingthe contacts 116 to the B contacts and placing the coils in opposition.Simultaneously, the coil current modulator switches the power switches154 on at a predetermined magnitude for the duration of the standbymode, thereby supplying continuous current flow the coil windings 110,112. The predetermined magnitude of the current is normally determinedby the average value of current supplied to the coil during the runmode. Therefore, during the standby mode, current is supplied to thecoil 70 in a manner as previously described with respect to the runmode. The opposing relationship of the coil windings 110, 112 preventsthe armature from being moved, and the dispensing valve remains closed.However, the power being supplied to the coil remains equal to the powersetpoint, and the temperature of the coil in the standby mode remainssubstantially constant. As will be appreciated, instead of applying aconstant current magnitude during the standby mode, alternatively, thepattern controller within the system control 130 provides output oftrigger pulses at a frequency that is equal to the maximum frequency ofthe trigger pulses that was stored during the learn mode, therebysupplying continuous current flow the coil windings 110, 112.

An alternative embodiment of the microprocessor control 137 isillustrated in FIG. 6. As will be appreciated, the power control 137 ofFIG. 4 requires two current/power conversions in the converters 138,146. Those current/power conversions must be performed in real time andutilize valuable processor time. The devices within the current control160 of FIG. 6 utilize only current, thereby eliminating the requirementfor the converters 138, 146. In a manner similar to that previouslydiscussed, during the learning mode, the current control 160 isimplemented with a microprocessor controller and stores a currentsetpoint value I_(sp) measured by the current sensor 128 when thedispensing system is operating at its maximum rate. Thus, the maximumdispensing rate is going to produce a desired maximum temperature of thecoil 70, and maintaining the current in the coil equal to the currentsetpoint will result in the coil 70 being maintained at a constanttemperature equal to the desired maximum temperature. Thereafter, duringthe run and standby modes, the A/D converter 136 provides a digitalsignal to the comparator or summing junction 141 which algebraicallyadds or compares the measured current value during the run and standbymodes with the current setpoint. If the measured current value isgreater than the current setpoint, a warning indicator or otherdiagnostic can be activated. The difference between those current valuesis provided as an error signal on the output 142 of the summing junction141. A feedback controller 162 utilizes a control loop such as a PIDcontrol to provide a signal to the waveform generator 164. The waveformgenerator 164 operates in a manner as previously described to modify thehold current, spike duration or peak current either individually or incombination to provide a drive signal to the D/A converter 149. The D/Aconverter 149 provides a signal on the output 151 to the currentmodulator 124 such that the current provided to the coil 70 ismaintained at the setpoint value. Thus, the temperature of the coil 70is maintained constant, and the coil temperature does not contribute tochanges in viscosity of the fluid being dispensed.

A still further embodiment of the thermal controller 126 is illustratedin FIG. 7A which uses a temperature control loop as opposed to a currentcontrol loop. A temperature setpoint T_(sp) is generally a function ofthe coil insulation system and may, for example, be 425° F. Thetemperature setpoint can selected by the user using input devicesassociated with the system control 130. Alternatively, the temperaturesetpoint can be automatically established in the learn mode by readingthe value of the temperature sensor 139 when the dispensing system isoperating at its maximum rate. The temperature sensor 139 can beimplemented with any known temperature sensing device, for example, aresistance temperature device, a thermocouple, a thermistor, a solidstate sensor, etc.

Thereafter, during the run and standby modes, a measured temperaturesignal is provided as an input to the summing junction 141. The summingjunction 141 algebraically adds or compares the measured temperaturevalue during the run and standby modes with the temperature setpoint. Ifthe measured temperature value is greater than the current setpoint, awarning indicator or other diagnostic can be activated. The differencebetween those temperature values is provided as an error signal on theoutput 142 of the summing junction 141. The feedback controller 162 andwaveform generator 164 operate in a manner as previously described tomodify the hold current, spike duration or peak current eitherindividually or in combination to provide a drive control signal to theD/A converter 149. The D/A converter 149 provides a comparable analogsignal on output 151 to the current modulator 124 such that the currentprovided to the coil 70 is regulated to maintain the temperature of thecoil 70 at the temperature setpoint value. Thus, the constant coiltemperature maintains a constant viscosity of the fluid being dispensed.

Another embodiment of the thermal controller 126 having a temperaturecontrol loop is illustrated in FIG. 7B. An A/D converter 133 has aninput connected to an output 123 of the power switches 154; and an A/Dconverter 135 has an input connected to an output 129 of the currentsensor 128. A temperature calculator 145 is responsive to the voltageand current signals from the respective A/D converters 133, 135 toprovide on its output 161 a signal representing a current, measuredtemperature of the coil 70. This embodiment can be used to determine thetemperature setpoint T_(sp) using either of the alternative off-timecurrent waveforms illustrated in FIGS. 2B-2C. In a learn mode, with thedispensing system operating at its maximum rate, after the temperaturecalculator 145 samples the voltage and current signals from the A/Dconverters 133, 135, the resistance of the coil can be computed inaccordance with Ohm's Law. The maximum temperature or temperaturesetpoint is then read from a table correlating coil resistance to coiltemperature that had been previously determined by experimentation aspreviously described.

The maximum temperature or temperature setpoint can alternatively bedetermined using the off-time waveform as previously described using thesinusoidal waveform of FIG. 2D. It should be noted that the initiationof the sinusoidal waveform of FIG. 2D is delayed for a short period oftime after the end of the on-time. That delay provides time for anycurrents induced by the collapsing electromagnetic field to dissipate.During the application of the sinusoidal waveform, the temperaturecalculator 145 detects a zero crossing of the voltage waveform on output123 of the power switches 154 (FIG. 1) that is applied to the coil 70.That zero crossing is used to start a timer or counter (not shown) inthe temperature calculator 145; and thereafter, the temperaturecalculator 145 detects the next zero crossing of the current waveform asdetected on the output 129 of the current sensor 128. That zero crossingof the current waveform is used to stop the counter; and therefore, thevalue measured by the counter in the temperature calculator 145represents a measured time shift between the voltage and current signalsthat are applied to the coil 70. The temperature calculator 145 usesthat measured time shift in conjunction with a table correlating timeshift to temperature that was created as previously described, and thetemperature calculator 145 provides on its output 161 a signalrepresenting the current temperature of the coil 70.

When the dispenser is operating in the run mode, the embodiment of FIG.7B can utilize any of the current waveforms illustrated in FIGS. 2B-2Dto continuously provide a measured temperature signal on the output 161of the temperature calculator 145. That measured temperature signal isprovided to the comparator 141 to produce an error signal therefrom andmodify the current waveform as described with respect to FIG. 7A tomaintain the temperature of the coil 70 at the desired temperaturesetpoint value.

Referring to FIG. 8, an alternative embodiment of the invention formaintaining a constant coil temperature is illustrated. In thisembodiment, a standard coil 71 is utilized and is connected to thecurrent sensor 128. A switching device 170, for example, a switchingrelay, has a switching solenoid 171 connected to switching contacts 172.As previously described with respect to FIG. 3, the thermal controller126 provides a run/standby signal on an output 127 as it is receivedfrom the system control 130. The run/standby signal is provided to theswitching solenoid 171 over the output 127 of the thermal controller126. In the run mode, the switching solenoid 171 moves the switchingcontacts 172 to the illustrated A position, thereby connecting the coil71 to the power switches 154. In the run mode, the gun controller 120operates in a manner substantially identical to that described withrespect to FIGS. 3-6. A drive current signal is provided to the coil 71that is derived from a current, power or temperature setpoint, whicheveris used.

When the thermal controller 126 detects that the operating mode has beenswitched to the standby mode, the state of the signal on the output 127is changed, thereby causing the switching solenoid 171 to switch thecontacts 172 to the B contacts. In this position, the coil 71 isconnected to a high frequency power supply 173. The output frequency ofthe high frequency power supply 173 is chosen to have a frequency valuehigher than the response time of the coil, that is, sufficiently highthat the coil 71 is incapable of moving the armature 60. If the highfrequency signal swings equally above and below an average value, thegun acts like a low pass filter. If the average value is zero, the gunwill not be actuated. Further, the frequency chosen should not permitthe coil 71 to dither the armature 60 and dispensing valve 33 to such anextent that the dithering action generates heat at the end of thedispensing gun 10 or permits minute quantities of fluid to pass throughthe dispensing valve 33. Therefore, such a frequency may be in a rangeof about 10 KHz or less to 1 MHz or more; but normally, the frequency isaround 100 KHz.

In a manner similar to that previously described with respect to powerswitches 154, the high frequency power supply 173 is responsive to theoutput 152 of summing junction 150 in order to vary the magnitude of thehigh frequency signal applied on the output 174 of the power supply 173.The net result is that the average or RMS current as detected by thecurrent sensor 128 and thermal controller 126 is maintained equal to therespective current, power or temperature setpoint during the standbymode of operation, thereby maintaining the temperature of the coil 71constant and hence, a more constant viscosity within the dispensing gun10.

Referring to FIG. 9, a further embodiment of the apparatus forcontrolling the temperature of the coil 71 is illustrated. The coil 71is mounted adjacent an armature 60 within a dispensing body 12. One ormore Peltier elements 176 are mounted on the exterior of the dispensingbody 12. A heat sink 177 is mounted over the Peltier element 176. APeltier element is a two-terminal bidirectional device capable ofheating or cooling by reversing the direction of current flow throughthe Peltier element. Peltier elements are commercially available fromMelcor of Trenton, N.J.

In one mode of operation, the gun controller 120 receives a run/standbysignal from the system control 130 and a waveform generator 165 createsa waveform similar to that described with respect to FIG. 2A. Thevariables associated with the waveform are determined in a traditionalmanner in that the peak current magnitude I_(pk) and peak currentduration T_(pk) are determined as a function of the viscosity of thefluid being dispensed. Further, the hold current I_(h) is determined tobe the minimum current required to hold the dispensing valve 33 open.That waveform is provided to the coil current modulator 124 and a drivecurrent signal is provided to the coil 71 in accordance with the outputfrom the waveform generator 165 and the feedback from the current sensor128 in a manner similar to that previously described. In thisembodiment, a temperature setpoint T_(sp) is provided to a summingjunction 179. The temperature setpoint may either be permanently storedwithin the gun controller 120 or provided in any of the ways previouslydescribed with respect to FIG. 7B including utilizing the currentwaveforms of FIGS. 2B-2D. The summing junction 179 compares thetemperature setpoint with a temperature feedback signal and provides asignal representing the difference between the inputs to a Peltierheat/cool control 181. The temperature feedback signal is provided inany one of several ways. For example, the temperature feedback signalmay be a temperature sensing device 175, shown in phantom, that ismounted in a heat transfer relationship with the coil 71. Thetemperature sensing device 175 can be any of several known devices, forexample, a temperature resistance device, thermal couple or other knowntemperature sensing device. Further, as will be appreciated, instead ofusing a separate temperature sensing device 175, the Peltier element 176can be used to sense the temperature. The heating/cooling cycles of thePeltier element 176 can be interrupted for short periods of time duringwhich the Peltier element 176 provides an output voltage proportional totemperature. Alternatively, the temperature feedback signal may beprovided by using any of the current waveforms of FIGS. 2B-2D aspreviously described. The Peltier control is a known heating control andmay be implemented using proportional, proportional integral or PIDcontrol to operate the Peltier element 176.

The temperature setpoint represents an expected temperature of the coil71 when the system is operating at a maximum rate. The Peltier heat/coolcontrol 181 is operative to cause the Peltier element 176 to selectivelyheat or cool the dispenser body 12 in response to the temperaturesensing device 175 detecting a temperature that is respectively lessthan or greater than the temperature setpoint. Thus, for example, if thesystem is operating at maximum rate in an environment that does notpermit proper cooling of the dispenser body 12, the dispenser body mayreach a temperature in excess of the desired temperature setpoint. Inthat situation, the Peltier heat/cool control 181 causes the Peltierelement 176 to cool the dispenser body 12 to the temperature setpoint.Alternatively, if the gun controller is switched from the run mode tothe standby mode in which no current is being supplied to the coil 71,the dispenser body cools to a temperature less than the temperaturesetpoint. That cooler temperature, as detected by the temperature sensor175, causes the Peltier heat/cool control 181 to operate the Peltierelement 176 to heat the dispenser body back to the temperature setpoint.

The use of the Peltier element 176 has the further advantage ofpermitting the coil to be operated in a power range, that is, at a rate,that exceeds its specified rate. For example, if the coil 71 isspecified to operate at a rate that is equivalent to nine watts of powerbeing applied to the coil and the Peltier element is capable of coolingthree watts of power from the coil, the coil current modulator 124 maybe used to drive the coil at a rate that is equivalent to twelve wattsof power, thereby substantially increasing the frequency of operation ofthe dispensing valve 33. Even though the coil is being supplied withtwelve watts of power, the Peltier element is able to remove three wattsof heat, thereby maintaining the net power heat of the coil 71 at ninewatts and within its specifications.

While the Peltier heat/cool control 181 is illustrated in FIG. 9 asbeing part of a closed temperature control loop utilizing thetemperature sensor 175, as will be appreciated, the temperature sensor175 may be eliminated and the Peltier heat/cool control operated in anopen loop mode responsive only to the temperature setpoint. Thetemperature control of FIG. 9 has further versatility in that, as willbe appreciated, the temperature setpoint may be fixed, user selectableto accommodate different sizes of coils, a constant value over time oreven a value that varies as a function of some other parameter.

The above embodiments of a coil temperature control for maintaining theconstant coil temperature have many advantages. First, the guncontroller does not rely on the user being able to select the bestcurrent waveform parameters, but instead, is adaptive and self-adjustingto maintain a constant coil temperature. With a constant coiltemperature, the viscosity of the fluid within the dispensing gun isheld more consistent, thereby improving the consistency of thedispensing process. Further, by maintaining the constant temperatureover the full range of operating frequency of the dispensing gun, thequality of the fluid dispensing operation is further enhanced and moreconsistent. Further, such a temperature control permits the dispensinggun to be consistently operated at a rate that is very close to, if notat, the theoretical maximum temperature limit of the gun withoutoverheating. The active temperature control protects the coil fromoverheating in the event that the user adjusts the current waveform suchthat an excessive temperature would otherwise be produced.

Further, by activating an overheat indicator when the measured feedbackcurrent or temperature exceeds the setpoint value, valuable feedback isprovided to the user with respect to the adverse effect of the selectedcurrent waveform parameters, thereby allowing the user to takeappropriate action.

Utilizing the dispensing valve coil to add heat to the module providesan opportunity for a new and different design of a dispensing gun.Referring to FIG. 1, the dispensing gun includes one or more valvedispensing modules 33 mounted onto a manifold 45. Normally, the manifold45 includes a heater and temperature feedback device (not shown) formaintaining the viscous fluid at a desired temperature. In the past, thecirculation of the heated fluid through the manifold 45 and dispensingvalve 33 proved to be an adequate thermal management strategy. However,as discussed earlier herein, the heat of the coil of the electric gunintroduces a new and significant thermal management issue. In accordancewith the principles of the present invention, by controlling the heatingof the coil, the temperature of the dispensing module or valve iscontrolled. Thus, for the first time, the thermal management of thedispensing module is self contained within the module and independent ofother elements, for example, the manifold plate 45. This new modulecapability provides new opportunities for a different construction ofthe dispensing gun.

Referring to FIG. 10, a dispensing gun 192 is constructed by seriallyconnecting dispensing valves or modules 193, 203 without requiring afluid distribution manifold 45 (FIG. 1) as is required in known fluiddispenser constructions. The modules 193, 203 are mounted immediatelyadjacent each other or are separated by a spacer plate 194 to providethe desired spacing between the nozzles 195 of the modules 193, 203. Inthe design of FIG. 1, the desired spacing of the modules 33 is achievedby mounting the modules 33 at the desired spacing on the manifold plate45.

A second distinction from known fluid dispensers is that the viscousfluid is fed serially through the dispensing modules 193, 203 from oneend of the dispensing gun 192. In contrast, in FIG. 1, each dispensingmodule 33 is fed directly from the manifold plate 45 by a dedicated feedpassage 49 within the manifold plate 45. The dispensing gun 192 of FIG.10 receives the viscous fluid from a feed member or end plate 196coupled to one end of the dispensing gun. The feed member 196 has afluid inlet 197 intersecting one side 210 of the member 196, and thefluid inlet is fluidly connected to a source of pressurized viscousfluid 47 (FIG. 1). The fluid inlet 197 is fluidly connected to a firstfluid passage portion 199 a that intersects an opposite side 211 of thefeed member 196. The opposite end of the dispensing gun 192 isterminated with a cap or end plate 198, the sole function of which is toterminate the continuous fluid passage 199 extending from the inlet 197,through the feed member 196, the dispensing valve 193, spacer plate 194and the dispensing valve 203. A second fluid passage portion 199 bwithin the dispensing module 193 intersects two sides, for example,opposite sides 212, 213 of the dispensing module 193. A third fluidpassage portion 199 c intersects two sides, for example, opposite sides214, 215 of the spacer plate 194, and a fourth fluid passage portion199d intersects two sides, for example, opposite sides 216, 217 of thedispensing module 203. As will be appreciated, the above constructionpermits the use of only a single dispensing module or any number ofdispensing modules as is required by the application. The spacer block194 can be of any width desired, or the dispensing modules 193, 203 canbe mounted together without an intervening spacer block 194. Inaddition, the cap 198 may be implemented by a plate or a plug that isthreaded into the passage 199 d at the side 217. Similarly, the feedmember 196 can be implemented with a plate, a nipple or other fittingthreaded into the passage 199 a at the side 210. Further, the internalfluid passages 199 b and 199 d can be L-shaped or T-shaped, so that thepassages 199 b, 199 d intersect other sides of the modules 193, 203,thereby providing more flexibility in designing a dispensing gun for aparticular application.

By incorporating heaters in the dispensing modules 193, 203 either byusing the coil as a heater or, by incorporating other heaters asdescribed with respect to FIG. 7A, the dispensing modules 193, 203 arecapable of providing sufficient heat to maintain the viscous fluidwithin the passage 199 at the desired temperature without requiring aseparate manifold. The construction of the dispensing gun 192 has thefurther advantage of being substantially more compact than thetraditional design of FIG. 1. Further, by eliminating the manifold 45 aswell as its associated heater and heat control apparatus, theconstruction of the dispensing gun 192 of FIG. 10 is substantially lessexpensive; and its simpler construction provides substantially greaterflexibility in mounting the dispensing gun 192 with associatedequipment.

The embodiments described thus far in FIGS. 2-9 are directed toproviding an automatic control of coil temperature to reduce the adverseeffects of varying coil temperature during the fluid dispensing process.As will be appreciated, in any application, providing the user with dataor indicators relating to an excessive temperature and a potentiallyexcessive temperature is also valuable. In many dispensing systems, theuser has the ability to manually adjust the peak current magnitudeI_(pk), the peak current duration T_(pk) and the magnitude of the holdcurrent I_(h). Further, the dispensing process involves many variablesthat are application dependent such as the dispensing pattern, theliquid viscosity, the production rate, the substrate material, etc. Inan effort to optimize the dispensing process, the user often changes theshape of the current waveform being provided to the coil. Further, theuser has no knowledge of when such adjustments come close to or exceedthe power specification or maximum temperature limit for the coil.Further, typical users generally do not have instruments, such as anoscilloscope or current probe, that would permit them to monitor thecurrent being supplied to the coil. Thus, a system that provides theuser with an indication of whether a chosen current waveform produces anexcessive coil temperature would be of significant benefit. Thus, whenadjusting the waveform of the current being supplied to the coil, theuser would have a real time feedback of whether such adjustments areapproaching or exceeding the maximum temperature limit of the coil.

FIG. 11 is on embodiment of such a thermal monitor and diagnosticcircuit. A measure of heating power in the coil is best represented by ameasurement of the RMS value of the current or voltage applied to thecoil. Such RMS values have a direct correspondence to coil heating andprovide a reasonable indication of temperature. As previously mentioned,the measurement of an RMS current value and its conversion to a directcurrent value can be effected either computationally or with aspecialized integrated circuit chip. One such integrated circuit chip isModel No. AD736 commerically available from Analog Devices. Other chipssuch as Model No. AD737 and AD637 as well as similar chips from othermanufacturers may also be used. Referring to FIG. 11, such an integratedcircuit chip 180 is responsive to coil current on an input 181 andprovides an output to red, yellow and green LEDs 182, 183, 184,respectively, that provide a qualitative indication of coil temperature.The coil current on the input 181 is provided to the chip 180 via aninput circuit 185 that includes a gain adjust potentiometer 186. Thechip 180 is powered by a power supply circuit 187, and the chip 180provides a DC signal on an output 188 that is proportional to the RMSvalue of the coil current supplied on the input 181. A comparatorcircuit 189 compares the magnitude of the DC voltage on the output 188to reference voltages that are selectable via potentiometers 190, 191.

The monitor circuit of FIG. 11 must be set for the temperaturecharacteristics of each different electric fluid dispenser. Thetemperature characteristics can be determined experimentally by storinga temperature versus power or current relationship for the fluiddispenser. Such a relationship can be determined by applying differentmagnitudes of current to the dispenser and measuring the resultanttemperature. The maximum temperature for the fluid dispenser is normallydetermined as a function of the manufacturer's specifications for thefluid dispenser. Using the stored current-temperature relationship, afirst current value can be determined based on the maximum dispensertemperature. That first current value is applied to the input 181, andthe potentiometer 190 is adjusted until the red indicator light 182turns on.

Similarly, a lesser temperature close to the maximum temperature, forexample, a temperature that is 90% or 95% of the maximum temperature, isselected. Using the stored temperature-current relationship, acorresponding current is determined and applied to the input 181 of themonitor circuit. Potentiometer 191 is then adjusted until a yellowcaution LED 183 is illuminated. Thus, the yellow caution LED 183indicates when the current in the coil is representative of atemperature between the lesser temperature and the maximum temperature.If the coil current on the input 181 is below the threshold of thecomparator circuit 189 necessary to illuminate the yellow LED 183, thegreen LED 184 is illuminated, thereby apprising the user that thecurrent waveform being selected by the user is less than the lessertemperature and will not produce an excessive coil temperature. WhileFIG. 11 illustrates one example of a coil temperature monitor, it shouldbe noted that the embodiments of FIGS. 3-9 all have the capability ofproviding a coil temperature monitor feature whether separatelyidentified as indicators 132 or integrated in the machine control 130.Further, the as shown in FIGS. 2B-2D, current sampling during theoff-time of the current waveform can also be used to provide atemperature monitor.

The thermal monitor circuit of FIG. 11 has the advantage of providingthe user with a real time indication of whether the user's adjustmentsto the current waveform provide a coil temperature that is less than,close to or in excess of the maximum coil temperature. Further, thespeed of a production line is often increased incrementally as variousadjustments are made and the increased speed does not adversely impactquality. As the line speed increases, the average coil currentincreases; and the monitor circuit of FIG. 11 continuously senses thecoil current and warns the user via the LEDs 182, 183 that the coilcurrent is close to or exceeds a value that produces an excessivetemperature. In addition, the thermal monitor uses an RMS value of coilcurrent or voltage and therefore, provides an excellent indicator oftemperature. In addition, the thermal monitor allows the user to selectthe temperature limits which are appropriate for the dispensing gunbeing used and the dispensing application being effected. As will beappreciated, other gradations of temperature may be provided, forexample, by a bar graph; and other forms of sensory perceptibleindicators, for example, audio indicators, may also be used.

While the present invention has been illustrated by a description ofvarious preferred embodiments and while these embodiments have beendescribed in considerable detail in order to describe the best mode ofpracticing the invention, it is not the intention of Applicant torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications within the spirit andscope of the invention will readily appear to those skilled in the art.For example, the run/standby signal is described as being userselectable and provided from the system control 130 to the thermalcontroller 126. As will be appreciated, the system control 130 canalternatively be used to directly drive the switching solenoid 171 andother components with the run/standby signal instead of the thermalcontroller 126. Further, other methods of providing a run/standby signalcan be readily derived. As will be appreciated, other signals, such assetpoint values, may originate in, or be stored in, the gun controller120 or the machine control 130 as is appropriate. Further, the guncontroller may also include user input and output devices as isappropriate and is generally a matter of design choice.

In the described embodiments with respect to FIGS. 3-9, the respectivepower, current and temperature setpoints were set to be representativeof the temperature of the coil with the system operating at a maximumdispensing rate. Further, warning indicators are activated in responseto the measured power, current or temperature exceeding the respectivepower, current or temperature setpoint. As will be appreciated, thesetpoint used in the control loop in the thermal controller 126 may beany temperature. Further, the thermal controller 126 may compare themeasured power, current or temperature to several reference values ofpower, current or temperature to provide other warning indicators. Forexample, the measured power, current or temperature values may becompared to a respective power, current or temperature setpointrepresenting a coil temperature at a chosen operating frequency or rateto control the waveform generator as described. In addition, themeasured power, current or temperature values may be compared to arespective power, current or temperature reference value representing amaximum coil temperature, and a warning indicator activated when themaximum coil temperature is exceeded.

The learn signal is described as being a user selected input to thesystem control 130, however, as will be appreciated, the learningprocesses may be implemented using other methods. For example, the guncontroller can, while the system is operating, keep track of the highesttrigger frequency and corresponding measured power, current ortemperature. Subsequently, the corresponding power, current ortemperature is defined as the setpoint value. Alternatively, the learnsignal can be avoided altogether by running the coil at the maximumpower, current or temperature that the gun can tolerate. In other words,the power, current or temperature setpoint is assumed to be the maximumfor the equipment rather than being application or installationspecific.

The switching device 114 of FIG. 3 provides a fixed switching of thecoil winding 112 with respect to the coil winding 110. Further, thepower switches 154 are effective to provide essentially the same drivecurrent to the coil 70 in both the run and the standby modes. Thus, therelationship between the heating power and the actuation force resultingfrom the current flow through the coil 70 in the run mode is equal tothe sum of the currents flowing through the coil windings 110, 112.However, the heating power provided by the current flow through the coil70 in both the run and standby modes is equal to the sum of the squareof the currents flowing through the coil windings 110, 112. In theswitching arrangement illustrated in FIG. 3, the coil windings 110, 112are serially connected by the switching device 114; and therefore, forany given drive current provided by the power switches 154, theactuation force and the heating power will have a fixed relationship. Ifthe coil windings 110, 112 were not serially connected, but wereconnected in parallel with respect to the power supply 122, then thecurrent flow through the coil winding 110 could be independentlycontrolled and different from the current flow in the coil winding 112.

Such a switching arrangement is illustrated in FIG. 12 as an alternativeembodiment of the coil current modulator 124. Power switches PS1-PS4connect each end of the coil windings 110, 112 to one side of the powersupply +V_(DC). Further, power switches PS5-PS8 connect each end of thecoil windings 110, 112 to the power supply common. Each of the powerswitches PS1-PS8 has a control input 202 connected to respective outputs1-8 of a switch controller 204. The switch controller is a logicprocessor that responds to a run/standby signal from output 140 of thesystem control 130 (FIG. 1) to connect the coil windings 110, 112 ineither an additive relationship or in opposition. For example, in therun mode, the switch controller 204 provides outputs to close powerswitches PS1, PS6, PS3 and PS8, thereby causing current to flow in thecoil windings 110, 112 in an additive relationship. When the standbymode is active, the switch controller 204 will provide outputs to openpower switches PS3 and PS8 and close power switches PS4 and PS7, therebyreversing the current flow with respect to the coil winding 112 andplacing the coil windings 110, 112 in opposition.

The switch controller 204 includes the further capability of varying theduty cycle of the operation of the power switches PS1-PS8 by utilizing,for example, a pulse width modulation process. Therefore, for example,if the power switches PS1 and PS6 are closed 100% of the time, a currentflow of 3 amps passes through coil winding 110. However, if, utilizingthe pulse width modulation capability of the switch controller 204, theduty cycle of the power switches PS1 and PS6 is reduced to 50%, thecurrent flow through the coil winding 110 is reduced to 1.5 amps. Usingthat capability, the following are several examples of how the heatingpower provided by the coil windings 110, 112 can be varied substantiallywhile maintaining a constant actuation force for opening the dispensingvalve.

In the first example, assume that during the run mode, the switchcontroller 204 operates the power switches at a 33% duty cycle.Continuing with the numerical examples of the prior paragraph, a 33%duty cycle results in 1 amp flowing through coil windings 110, 112 inresponse to power switches PS1, PS6, PS3 and PS8 being closed. Theactuation force is determined by the sum of the current flows throughthe coil windings 110, 112 and is therefore, 2 amps. Further, the powerheating capability is equal to the sum of the square of the currentflowing through the coil windings 110, 112 and is also 2 amps. The sameresult is achieved in the standby mode when power switches PS3 and PS8are opened and power switches PS4 and PS7 are closed.

In a second example, assume that in the run mode, power switches PS1 andPS6 are operated at a 67% duty cycle to provide 2 amps of current flowthrough coil winding 110, whereas power switches PS3 and PS8 areoperated at a zero duty cycle, thereby providing no current flow throughcoil winding 112. Once again, the actuation force resulting from the sumof the current flows is 2 amps. However, the heating power, which is aresult of the sum of the square of the current flows, is equal to 4amps. In the standby mode, power switches PS1, PS6, PS4 and PS7 areoperated at a 47% duty cycle providing a current flow of approximately1.4 amps through the coil windings 110, 112. Since the coil windings areconnected in opposition, the sum of the current flows is zero and theactuation force is likewise zero. However, the sum of the squares of thecurrent flows is approximately 4 amps which is the same as the heatingpower provided during the run mode.

In a third example, during the run mode, power switches PS1 and PS6 areoperated at a 100% duty cycle providing a 3 amp current flow throughcoil winding 110. In addition, power switches PS4 and PS7 are operatedat a 33% duty cycle providing a current flow of 1 amp through coilwinding 112. The coil windings 110, 112 are connected in opposition; andtherefore, the 1 amp flow through coil winding 112 subtracts from the 3amp flow through coil winding 110 to provide a net sum of a 2 ampactuating force. However, the power heating capability, being the sum ofthe squares of the currents, is approximately 10 amps. In the standbymode, the power switches PS1, PS6, PS4 and PS7 are operated at a 75%duty cycle to provide opposing current flows in coil windings 110, 112of 2.25 amps. The equal opposing current flows sum to a zero currentflow and a zero actuation force, however, the sum of the squares of thecurrent flows is approximately 10 amps.

The power switches PS1-PS8 are implemented using commercially availablesemiconductor switches several types of which have been previouslyidentified herein. The modulation of the operation of the power switchesPS1-PS8 to vary their duty cycle occurs at a frequency that issubstantially greater, for example, 100 times greater, than the maximumexpected frequency of the current waveforms provided on the output 152of the summing junction 150. As will be appreciated, otherconfigurations of power switches can be implemented, for example, thepower switches PS2 and PS5 can be eliminated from the circuit. The powerswitching circuit of FIG. 12 provides a substantial range of temperaturecontrol as well as significant design flexibility and precision in thecontrol of temperature of the gun coil. Further, the ability tomanipulate the temperature of the gun coil during the run and standbymodes is also substantially more flexible. By uncoupling the heatingcapability of the coil from the actuation force required to operate thecoil, a substantially wider range of heat control is possible.

In the embodiments described with respect to FIG. 3-9 and 12,temperature control is obtained by maintaining a constant temperatureduring both the run and standby modes of operation, that is, both, whilethe dispensing gun is dispensing fluid, and while the dispensing gun isinactive and not dispensing fluid. Maintaining a constant coiltemperature during all modes of operation theoretically provides thebest results and the least impact on the quality of the dispensingoperation, but it comes at a substantial price in terms of additionalcomponents and complexity to the dispensing control system. For example,in the described embodiments, such components may include a bifilar coiland associated switching circuits or, alternatively, a high frequencypower supply and associated switching circuits, etc.

An alternative embodiment is illustrated in FIG. 13 in which atemperature control is provided by maintaining a constant temperatureduring only the run mode of operation. The embodiment of FIG. 13 isidentical to the embodiment of FIG. 3 except that there is no bifilarcoil and coil switching circuits, and thus, the operation of theapparatus of FIG. 13 is identical to the operation of the apparatus ofFIG. 3 except with respect to the standby mode of operation. Theembodiment of FIG. 13 does not heat the coil 70 during the standby modeof operation. The embodiment can be operated in a learn mode todetermine a maximum current or power being consumed by the dispensinggun to establish a power, current or temperature setpoint. In the runmode of operation, a current feedback is provided to the thermalcontroller 126, and a waveform generator 148 as previously describedprovides a stepped current waveform to the coil current modulator 124.The coil current modulator 124 provides a drive current to the coil 70to maintain a current or power in the coil substantially equal to therespective current or power setpoint. Thus, the coil 70 is firstoperative to actuate the dispensing valve 33 (FIG. 1) to dispense thefluid and is used simultaneously as a heater in the run mode to maintainthe temperature of the coil generally constant. As previously described,the values of the peak current I_(pk), hold current I_(h), time widthT_(pk) and other current waveform variables, may be adjusted to changethe RMS value of the current being supplied to the coil 70. As will alsobe appreciated, all of the different embodiments of the thermalcontroller 126 illustrated and described with respect to FIGS. 4, 6, 7and 9 including the use of current sampling during the off-time of thecurrent waveform as shown and described with respect to FIGS. 2B-2D areequally applicable to the embodiment of FIG. 13. Hence, the thermalcontroller 126 of FIG. 13 can be implemented with a power control loopas described with respect to FIG. 4, with a current control loop asdescribed with respect to FIG. 6, or with a temperature control loop asillustrated in FIGS. 7A and 7B. Alternatively, a Peltier device 181(FIG. 9) can be used only in the run mode to maintain the coil at aconstant temperature.

Thus, the embodiment of FIG. 13 maintains the coil 70 at a desiredtemperature during the run mode of operation; and during the run mode,all of the advantages of having a constant temperature dispensing gunare realized by using the embodiment of FIG. 13. With the embodiment ofFIG. 13, the temperature of the coil 70 and the dispensing gun 10 mostprobably decreases during the standby mode. And, when the run mode isagain activated, the temperature of the coil 70 and the dispensing gun10 increases until it reaches the desired value. Thus, the embodiment ofFIG. 13 allows for some temperature variations and the disadvantagesassociated therewith. However, the embodiment of FIG. 13 in providingfor temperature control during only the run mode provides many of thepreviously described advantages over known devices.

Further, the embodiments illustrated with respect to FIGS. 3-7 and 13are described as being implemented using digital processors and/orcontrollers; however, as will be appreciated, one skilled in the art maychoose to implement portions or the entirety of those embodiments withanalog devices.

Therefore, the invention in its broadest aspects is not limited to thespecific detail shown and described. Consequently, departures may bemade from the details described herein without departing from the spiritand scope of the claims which follow.

What is claimed is:
 1. An electrically operated fluid dispenser fordispensing a viscous fluid onto a substrate comprising: a first bodycomprising a fluid passage having a first end intersecting a first sideof said first body, said first end of said fluid passage adapted toreceive the viscous fluid directly from a source of pressurized fluid,and a second end intersecting a second side of said first body, saidsecond end of said fluid passage not receiving the viscous fluiddirectly from the source of pressurized fluid, and an outlet in fluidcommunication with said fluid passage; a first armature disposed in saidfirst body and movable between an opened position allowing a fluid flowfrom said outlet and a closed position preventing the fluid flow fromsaid outlet; a first coil mounted adjacent said first armature andselectively generates an electromagnetic field capable of moving saidfirst armature between the opened and closed positions; and a firstheater for maintaining said first coil at a substantially constanttemperature.
 2. An electrically operated fluid dispenser of claim 1wherein said first heater comprises said first coil being energized by acurrent in said coil.
 3. An electrically operated fluid dispenser ofclaim 1 wherein said first heater comprises a heating and cooling heattransfer device mounted in a heat transfer relationship to said firstcoil.
 4. An electrically operated fluid dispenser of claim 1 furthercomprising: a feed member having a fluid passage intersecting first andsecond ends of said feed member, said first end of said feed memberbeing mounted to said first side of said first body with one end of saidfluid passage in said feed member fluidly connecting with said first endof said fluid passage in said first body.
 5. An electrically operatedfluid dispenser of claim 4 further comprising a cap mounted to saidsecond side of said first body and terminating said fluid passage atsaid second opening on said second side of said first body.
 6. Anelectrically operated fluid dispenser of claim 4 further comprising: asecond body having a fluid passage intersecting first and second sidesof said second body and an outlet in fluid communication with said fluidpassage, said first side of said second body being mounted against saidsecond side of said first body with one end of said fluid passage insaid second body fluidly connecting with an opposite end of said fluidpassage in said first body; a second armature disposed in said secondbody for movement between an opened position allowing a fluid flow fromsaid outlet and a closed position preventing the fluid flow from saidoutlet; a second coil mounted adjacent said second armature andselectively generates an electromagnetic field capable of moving saidsecond armature between the opened and closed positions; and a secondheater for maintaining said second coil at a substantially constanttemperature.
 7. An electrically operated fluid dispenser of claim 6further comprising a spacer plate having a fluid passage intersectingfirst and second sides of said spacer plate, said first side of saidspacer plate being disposed against to said second side of said firstbody with one end of said fluid passage in said spacer plate fluidlyconnecting with an opposite end of said fluid passage in said firstbody, and said second side of said spacer plate being disposed againstsaid first side of said second body with one end of said fluid passagein said second body fluidly connecting with an opposite end of saidfluid passage in said spacer plate.
 8. An electrically operated fluiddispenser of claim 6 wherein said first and second heaters comprise saidfirst and second coils, respectively, being energized by currents insaid respective first and second coils.
 9. An electrically operatedfluid dispenser of claim 6 wherein said first and second heaterscomprise first and second heating and cooling heat transfer devicesmounted in a heat transfer relationship to said first and second coils,respectively.
 10. An electrically operated fluid dispenser of claim 6further comprising a cap mounted to said second side of said secondfirst body and terminating said fluid passage at said second side ofsaid second body.
 11. An electrically operated fluid dispensercomprising: a first body having a fluid passage intersecting first andsecond sides of said first body and an outlet in fluid communicationwith said fluid passage; a first armature disposed in said first bodyand movable between an opened position allowing a fluid flow from saidoutlet and a closed position preventing the fluid flow from said outlet;a first coil mounted adjacent said first armature and selectivelygenerates an electromagnetic field capable of moving said first armaturebetween the opened and closed positions; and a first heater formaintaining said first coil at a substantially constant temperature; afeed member having a fluid passage intersecting first and second ends ofsaid feed member, said first end of said feed member being mounted tosaid first side of said first body with one end of said fluid passage insaid feed member fluidly connecting with one end of said fluid passagein said first body; and a cap mounted to said second side of said bodyand terminating said fluid passage on said second side of said firstbody.
 12. An electrically operated fluid dispenser comprising: a firstbody having a fluid passage intersecting first and second sides of saidfirst body and an outlet in fluid communication with said fluid passage;a first armature disposed in said first body and movable between anopened position allowing a fluid flow from said outlet and a closedposition preventing the fluid flow from said outlet; a first coilmounted adjacent said first armature and selectively generates anelectromagnetic field capable of moving said first armature between theopened and closed positions; and a first heater for maintaining saidfirst coil at a substantially constant temperature; a second body havinga fluid passage intersecting first and second sides of said second bodyand an outlet in fluid communication with said fluid passage, said firstside of said second body being mounted adjacent said second side of saidfirst body with one end of said fluid passage in said second bodyfluidly connecting with an opposite end of said fluid passage in saidfirst body; a second armature disposed in said second body for movementbetween an open position allowing a fluid flow from said outlet and aclosed position preventing the fluid flow from said outlet; a secondcoil mounted adjacent said second armature and selectively generates anelectromagnetic field capable of moving said second armature between theopen and closed positions; and a second heater for maintaining saidsecond coil at a substantially constant temperature.
 13. An electricallyoperated fluid dispenser of claim 12 wherein said first side of saidsecond body being disposed against said second side of said first body.14. An electrically operated fluid dispenser of claim 12 furthercomprising a cap being disposed against said second side of said secondbody and terminating said fluid passage at said second opening on saidsecond side of said second body.
 15. An electrically operated fluiddispenser of claim 12 further comprising a spacer plate having a fluidpassage intersecting first and second sides of said spacer plate, saidfirst side of said spacer plate being disposed against said second sideof said first body with one end of said fluid passage in said spacerplate fluidly connecting with an opposite end of said fluid passage insaid first body, and said second side of said spacer plate beingdisposed against said first side of said second body with one end ofsaid fluid passage in said second body fluidly connecting with anopposite end of said fluid passage in said spacer plate.
 16. Anelectrically operated fluid dispenser of claim 12 wherein one of saidfirst and second heaters comprises a respective one of said first andsecond coils being energized by a current in said respective one of saidfirst and second coils.
 17. An electrically operated fluid dispenser ofclaim 12 wherein one of said first and second heaters comprises aheating and cooling heat transfer device mounted in a heat transferrelationship to a respective one of said first and second coils.